It can be extremely important to have as an alternative some means of manual propulsion for watercraft in the event of motor failure or absence of wind. In the past various types of oars and paddles have served to propel boats through the water in such circumstances. However, such conventional paddles and oars are ineffective in propelling larger pleasure craft, such as motor launches, cabin cruisers and sailing yachts.
In many cases, there is simply no place on such craft from which a sailor can effectively use a paddle or oars. The maximum propulsive force that can be obtained with a conventional paddle is relatively minor compared to the forces resisting propulsion arising from water pressure against the hull, wind, inertia and so forth. Furthermore, it is very difficult in such craft to direct the little propulsive force that can be obtained with a paddle in a suitable direction to propel the craft in a direct course. Typically, paddling causes the boat to rotate, rather than to move forwards.